1. Field of the Invention
This invention relates generally to devices for interventional therapeutic treatment or vascular surgery for treatment of defects in the vasculature, and more particularly concerns a system and method for delivering intravascular interventional devices, such as for treatment of aneurysms.
2. Description of Related Art
Vascular interventional devices such as vasoocclusive devices are typically placed within the vasculature of the human body by use of a catheter. Vascular interventional devices such as stents can be placed within an occluded vessel to facilitate blood flow through the vessel, and vasoocclusive devices are typically either placed within a blood vessel to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus, or are placed within an aneurysm stemming from the vessel to form such an embolus within the aneurysm. Stents can have a wide variety of configurations, but generally need to be placed and then released at a desired location within a blood vessel. Vasoocclusive devices used for these procedures can also have a wide variety of configurations, and aneurysms have been treated with external surgically placed clips, detachable vasoocclusive balloons and embolus generating vasoocclusive devices such as one or more vasoocclusive coils.
The delivery of such vasoocclusive devices have typically been accomplished by a variety of means, including via a catheter in which the device is pushed through an opening at the distal end of the catheter by a pusher to deploy the device. The vasoocclusive devices can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm.
Some conventional vasoocclusive devices are operated by pulling or jerking the catheter tip from the balloon, thus potentially compromising the position of the implant. One such device provides for an endovascular wire and tip that can be separated from the holding wire mechanically or electrolytically for the formation of thrombus in blood vessels. However, such devices that release the interventional device by mechanically breaking an intermediate section between the catheter tip and balloon can potentially leave broken or jagged ends that can potentially injure the vasculature.
One conventional releasable balloon catheter used to embolize vascular lesions has a tube portion made of a material such as a hydrophilic polymer, located between the catheter and the balloon, that can be broken by torsion of the tube. The tube can be melted by heating the tube, or can be dissolved in the blood when heated, and electrodes are provided for heating the tube. Another conventional technique for separating a balloon from a balloon catheter involves the melting and breaking of a connecting member made from polyvinyl alcohol or trans-polyisoprene between the balloon and the catheter body, when power is supplied to electrodes provided for heating the connecting member. When the connecting member is heated to temperatures of about 70xc2x0 C. and slight tension is applied, the balloon can be separated from the main catheter body. However, such devices that release the interventional device by melting or dissolving the intermediate section between the catheter tip and balloon can also potentially release undesirable particles of materials into the bloodstream.
There is therefore a need for a precise method of deploying therapeutic interventional devices without compromising the position of the implant, without presenting broken or jagged ends that can potentially injure the vasculature, and without releasing undesirable particles of materials into the bloodstream.
The transmittal of energy of various types through a catheter to a remote location in the body has been used in the past, both for therapeutic purposes and to perform actuation or chemical reactions for delivery systems. In one such system, a temporary stent formed from a coil of tubular thermoplastic material is delivered activated for use by a heating element. The thermoplastic stent body is introduced into the vessel to be supported and is then heated by the heating element above its softening temperature and expanded to a second dimension in order to support the vessel. Cooling of the stent body allows the stent to temporarily support the vessel, and the stent body can be heated at a later time to soften and remove the stent from the vessel. However, the thermoplastic stent body contains an electrical resistance heating element, and heat is generated in the stent by a current is passed through electrically conductive wires.
An endovascular stent and delivery system is also known in which a partially cured material is delivered to a selected site in a blood vessel and is then crosslinked in the blood vessel by laser light energy delivered to the partially cured material. The delivery system can also use thermal energy as from a resistive heating element, radio frequency energy, or beta rays in order to cause the crosslinking.
A flexible guide is also known that is formed from a two-way shape memory alloy for use in non-invasive procedures. The device comprises an elongated, flexible guide having a core of a shape memory alloy which allows for tip-deflection and rotational movement to the guide wire in response to heating provided by transmission of an electrical current through the shape memory alloy.
Another catheter is known that is composed of a main body fitted with a shape memory alloy, with a liquid injector for supplying a warming liquid such as a physiological saline or transfusion solution when the shape memory alloy is to recover an original shape.
In another delivery system for an occlusive device, energy is transmitted through a catheter to a coil and a polymeric material to occlude an aneurysm. The polymeric material is solidified by light, heat or RF energy emitted from the end of a light or energy emitting device placed outside the distal end of the guiding catheter.
A common problem with such known delivery and activation systems, conveying heat by such methods as warm liquids, light, electrical energy, radio frequency energy or beta rays, is that they are typically highly inefficient or not particularly powerful, so that once a device to be delivered is placed in the desired location, there can be a delay while sufficient thermal energy is conducted to the activation site, or in the process heat energy can be radiated or otherwise lost during transmission. It would therefore be desirable to provide a thermal energy activated delivery system for vascular interventional devices that is highly efficient and immediate, and can allow the delivery of a necessary amount of thermal energy to a specific location for deployment of an interventional device.
Heat pipes are known as extremely efficient heat transfer devices, and are much more efficient than solid metal heat sinks, for example. Such heat pipes typically have a hollow interior chamber that has been evacuated, then filled with a small amount of working fluid, and sealed. When heat is applied to one end, serving as an evaporator end, the fluid vaporizes, and carries the heat in the vaporized working fluid extremely rapidly to the other end, serving as a condenser end, where the latent beat of vaporization is released as the vapor condenses back into liquid form. The working fluid is then carried back in liquid form to the evaporator end by capillary action. There is thus a need for application of a flexible heat pipe for conducting heat to a specific desired site for the purpose of deploying interventional devices such as stents and occlusive devices. The present invention meets these and other needs.
Briefly, and in general terms, the present invention provides a precise system and method for efficiently and cleanly releasing a therapeutic device such as a vasoocclusive coil, a stent, or other therapeutic device for use in interventional therapy and vascular surgery, and which is particularly adapted to be inserted into a portion of a vasculature for treatment of a body vessel such as an aneurysm without compromising the position of the implant.
In a presently preferred aspect of the invention, the intravascular delivery system for release and deployment of a therapeutic device within the vasculature of a patient comprises an elongated, flexible heatpipe pusher member; a therapeutic device to be placed within the vasculature of a patient; and a shape memory device detachably mounting the therapeutic device for placement of the therapeutic device within the vasculature, the shape memory device having a closed configuration connecting the therapeutic device to the flexible heat pipe pusher member, and an open configuration for detaching and deploying the therapeutic device from the flexible heat pipe pusher member when a desired placement of the therapeutic device within the vasculature is achieved. The shape memory device is typically a shape memory collar disposed on one of the therapeutic device and the flexible heat pipe pusher member and connects the therapeutic device and the heat pipe pusher member, and in a presently preferred embodiment, the shape memory device is a shape memory collar disposed on the distal tip of the flexible heat pipe pusher member and connecting the therapeutic device to the flexible heat pipe pusher member. In a presently preferred embodiment, the shape memory collar is made of nickel titanium alloy.
In a presently preferred aspect of the invention, the elongated, flexible heat pipe pusher member comprises a flexible heat pipe having a hollow interior chamber containing a working fluid, the flexible heat pipe having a metal evaporator end portion for conducting heat to the working fluid in the interior chamber of the heat pipe, a flexible insulated mid-portion, and a metal condenser end portion for conducting heat from the working fluid to the shape memory device. In another presently preferred aspect, the insulated mid-portion comprises an outer covering of resinous material so that the mid-portion does not radiate heat. The flexible heat pipe typically comprises a metal hollow tube, and in a presently preferred embodiment, the metal hollow tube is formed from a beryllium copper alloy. In another presently preferred aspect, the evaporator end portion comprises a stainless steel portion for conducting heat to the metal hollow tube and the working fluid in the interior chamber of the heat pipe, and the condenser end portion is partially covered with polytetrafluoroethylene, leaving a distal end portion of the condenser end portion exposed to transfer heat to the shape memory collar.
The shape memory collar can be heated to thereby assume a configuration disconnecting the therapeutic device and the flexible heat pipe pusher member, and the heat pipe pusher member advantageously can be connected to a heat source for transferring heat to the collar to induce the collar to detach the therapeutic device from the flexible heat pipe pusher member. In one presently preferred embodiment, the therapeutic device comprises a stem, and the collar clamps onto the stem. The therapeutic device can comprise a vasoocclusive coil, a stent, or another similar therapeutic device adapted to be placed in the vasculature.
The invention thus also provides for a method for release and deployment of a therapeutic device within the vasculature of a patient. In a presently preferred embodiment, the steps of the method comprise providing a therapeutic device to be placed within the vasculature of a patient; providing an elongated, flexible heat pipe pusher member; providing a shape memory device; detachably mounting the shape memory device to one of the therapeutic device and the elongated, flexible heat pipe pusher member, the shape memory device having a closed configuration connecting the therapeutic device to the flexible heat pipe pusher member, and an open configuration for detaching and deploying the therapeutic device from the flexible heat pipe pusher member when a desired placement of the therapeutic device within a patient""s vasculature is achieved; positioning the therapeutic device at a desired placement within a patient""s vasculature; and disconnecting the therapeutic device from the elongated, flexible heat pipe pusher member, thereby deploying the therapeutic device. In a presently preferred aspect of the method of the invention, the step of disconnecting the therapeutic device from the elongated, flexible heat pipe pusher member comprises causing heat to be transmitted through the flexible heat pipe member to the shape memory collar to heat the shape memory collar to cause the shape memory collar to expand to release the therapeutic device.
The present invention also provides for an apparatus for release and deployment of a therapeutic device within the vasculature of a patient, comprising an elongated, flexible pusher member having an interior lumen and a distal portion, and a connector fiber detachably mounting the therapeutic device to the pusher member for placement of the therapeutic device within the vasculature, the connector fiber being capable of being broken by heat. An elongated, flexible heat pipe member is disposed within the interior lumen of the elongated, flexible pusher member, and has a distal heating end disposed adjacent to the connector fiber for heating the connector fiber to cause the connector fiber to break and release the therapeutic device for detaching and deploying the therapeutic device from the flexible pusher member when a desired placement of the therapeutic device within the vasculature is achieved. In a presently preferred aspect, the connector fiber is formed from a thermoplastic material, such as polyethylene. In another presently preferred aspect, the pusher member includes at least one entry port communicating with the interior lumen of the pusher member, and the distal heating end of the heat pipe member is disposed in the interior lumen of the pusher member adjacent to the at least one entry port. In a preferred embodiment, the connector fiber extends from a proximal portion of the pusher member to form a loop through the connector ring, and back through the at least one port through the pusher member to the proximal portion of the pusher member. In another preferred aspect, the therapeutic device to be placed within the vasculature of a patient is connected to an annular connector ring, and the connector fiber mounting the therapeutic device to the pusher member passes through the connector ring to secure the therapeutic device to the pusher member.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.